Results demonstrated that rabbit

serum has a chitinase activity, Osimertinib molecular weight as both 4-MUF GlcNAc2 and 4-MUF GlcNAc3 were cleaved in the presence of serum or with BSK-II supplemented with 7% serum (Table 1). Interestingly, rabbit serum did not cleave the 4-MUF GlcNAc substrate (Table 1), indicating that it does not contain a β-N-acetylglucosaminidase activity. Next, we inactivated the chitinase activity in rabbit serum by boiling so that a chitinase-free medium could be used to evaluate growth of B. burgdorferi on chitin substrates. Rabbit serum was diluted (2-fold) with sterile water prior to boiling (see Methods) as undiluted serum solidified when boiled. Boiling for a total of 10 minutes (5 × 2 min) completely inactivated chitinase find more activity in rabbit serum (Table 1). Table 1 Chitinase activitya in rabbit serum. Treatment 4-MUF GlcNAc 4-MUF GlcNAc2 4-MUF GlcNAc3   Average b (± SE) c Average(± SE) Average (± SE) Serum       Not Boiled

5.6 (± 3.0) 9,279.7 (± 1,321.6) 17,718.9 (± 6,559.2) Boiled 5.3 (± 2.2) 12.8 (± 3.6) 16.3 (± 5.2) BSK + 7% Serum       Not Boiled 9.3 (± 4.7) 2,610.6 (± 895.5) 2,931.1 (± 170.0) Boiled 11.0 (± 4.9) 14.3 (± 8.2) 28.2 (± 14.5) a Chitinase activity was measured as relative fluorescence units b Average activity of 3 replicate experiments. c SE, standard error of the mean Growth of wild-type B. burgdorferi on chitin Inactivating

the chitinase activity in rabbit serum allowed us to perform growth experiments to determine if B. burgdorferi possesses a chitinase activity and can utilize chitin in the absence of free GlcNAc. Previous reports by our laboratory [17] and others [14, 15] demonstrated that B. burgdorferi exhibits biphasic growth when cultured in the absence of free GlcNAc, and that chitobiose can substitute for free GlcNAc resulting in growth to maximum cell density in a single exponential Clostridium perfringens alpha toxin phase. We repeated those experiments here using BSK-II lacking GlcNAc and supplemented with 7% boiled rabbit serum. As shown in Fig. 1, boiling the serum did not have an adverse effect on cell growth. In addition, when cells were cultured in the presence of 50 μM chitotriose, 25 μM chitohexose or 0.4% coarse chitin flakes, maximum cell densities were reached in a single exponential phase, similar to growth on 1.5 mM GlcNAc or 75 μM chitobiose (Fig. 1). These results demonstrate for the first time that B. burgdorferi can use GlcNAc oligomers (longer than chitobiose) and chitin in the absence of free GlcNAc. Figure 1 Chitin utilization in medium supplemented with boiled rabbit serum. Wild-type cells (B31-A) were cultured in BSK-II without GlcNAc and supplemented with 7% boiled rabbit serum. Late-log phase cells were diluted to 1.